FWIW, after stupidly trying to adjust a 2x9 lever to a triple crank yesterday (I had forgotten the levers were not 3x), I had to tune out the 30t to make it work, and work it did. 42t even around here is plenty with a 12-27.
Why not 53/42 with a 14-25 in the back for 9 speed?
I know I couldn't climb in CO with a 42x27 bottom gear. Of course, you may be stronger and lighter than I am, or just ride east.